This invention relates to an information medium which can be clearly identified, and is thus easily distinguishable from other similar information media.
Such information media are usually available in the form of cards. Each has a memory for storing personal data about its owner. Upon receipt of instruction information from an external device, it sends corresponding data to the external device. The external device decodes the received data and can identify the information medium by means of the decoded data.
U.S. Pat. No. 4,641,374 discloses to the inventor hereof the basic structure of the above-mentioned information medium. The medium claimed in the United States patent does not have hardware components, such as a CPU for controlling a large amount of data.
The conventional information medium has tended to use a standard hardware circuit, to decode external instructions. Hence, the same code pattern is used for all of the media provided with the same instruction-decoding circuit. This allows the owner of one information medium to be able to know the data stored within other media of the same type, in addition to that stored in his or her own information medium.
To prevent this situation from occurring, it is necessary to change the code pattern for each information medium. However, the instruction-decoding circuit is a hardware device, and this inevitably requires that the design of the circuit be altered for each information medium.
Moreover, surrounding noises have sometimes caused the information medium to malfunction. To resolve this problem, the code pattern can be lengthened, to reduce the chance of a malfunction occurring. It has, however, proved difficult to lengthen the code pattern, since the pattern is defined by the hardware; more precisely, by the circuit for decoding external instruction information.
Some of the conventional information media use electric waves or light beams, to transmit data. Media of this type usually have a dry cell provided within them, to supply power to their internal circuits. Consequently, strong demand has arisen for an information medium of this type to be developed, which consumes less power and which can function efficiently.